Active magnetic bearing with automatic detection of the position thereof

Abstract

An active magnetic bearing (100) with autodetection of position, the bearing comprising at least first and second opposing electromagnets (120, 130) forming stators disposed on either side of a ferromagnetic body (110) forming a rotor and held without contact between said electromagnets. The first and second electromagnets (120, 130) each comprising a magnetic circuit (121; 131) essentially constituted by a first ferromagnetic material and co-operating with said ferromagnetic body to define an airgap, together with an excitation coil (122; 132) powered from a power amplifier whose input current is servo-controlled as a function of the position of the ferromagnetic body relative to the magnetic circuits of the first and second electromagnets. The position of the ferromagnetic body (110) being measured from the inductance detected between the two electromagnets (120, 130) in response to simultaneous injection into both opposing electromagnets of a sinusoidal current at a frequency that is greater than the closed loop passband of the system. The magnetic circuit (121; 131) of each electromagnet further includes a portion (124; 134) in the vicinity of the excitation coil (122; 132) that uses a second ferromagnetic material having magnetic permeability that is lower than that of the first material and electrical resistivity that is higher than that of the first material so as to encourage the passage of the high frequency magnetic fields that are generated in the bearing.

Description

[0001]This application is a 371 national phase filing of PCT / FR2005 / 000626 filed Mar. 16, 2005, and claims priority to French application No. 04 02902 filed Mar. 22, 2004.FIELD OF THE INVENTION[0002]The present invention relates to active magnetic bearings in which, in addition to their bearing function proper, a detection function of the inductive type is also performed, with this being done without adding any electromagnetic circuit or any amplifier other than those used for performing the bearing function.PRIOR ART[0003]Integrating the function of detecting the position of the suspended body in an active magnetic bearing, known as a bearing with autodetection, presents numerous advantages in terms of cost, rationalization, and precision of detection in comparison with more conventional systems in which the position of the suspended body, such as a rotor or a disk, is measured using position detectors that are distinct from the elements of the driving bearing for producing the for...

AI Technical Summary

Benefits of technology

The present invention aims to solve the problems of current magnetic bearings by providing an active magnetic bearing with autodetection that guarantees a sufficient level of inductance (coupled with the airgap) regardless of external sources of disturbance such as the dimensions and current of the bearing. The bearing includes at least first and second opposing electromagnets forming stators disposed on either side of a ferromagnetic body forming a rotor and held without contact between the electromagnets. The position of the ferromagnetic body is measured from the inductance detected between the two electromagnets in response to simultaneous injection into both opposing electromagnets of a sinusoidal current at a frequency that is greater than the closed loop passband of the system. The magnetic bearing structure includes a portion of permeability and resistivity that are adapted to "channel" the high frequency magnetic field lines used for autodetection of position in the bearing. This guarantees inductance values at high frequency that are well defined independently of the dimensions of the bearing and of the current fed thereto. The bearing can be used for both axial and radial types.

Problems solved by technology

Although the device described in U.S. Pat. No. 5,844,339 operates in satisfactory manner, it nevertheless presents certain limitations that prevent its field of action from being enlarged.

The cost of the associated electronics depends on its complexity and also and above all on the performance required of the bearing power amplifiers.

Under such circumstances, the principle of an autodetection bearing is difficult to achieve.

In practice, this coupling falsifies the position information and increases sensitivity as a function of frequency (generating noise in the servo-control).

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